A comparison of the a.c. energy losses of Nb-Ti composite superconduct
ors at various time intervals over several years is carried out. The o
bserved decrease of eddy current losses by a factor of 1.4-3.4 is prob
ably associated with increasing effective transverse resistivity of th
e matrix due to diffusion between Nb-Ti and copper. The processes of a
ging did not result in a decreasing current-carrying capability.